The present invention relates to retractable packing components for rotary machines such as steam and gas turbines.
Rotary machines such as steam and gas turbines used for power generation and mechanical drive applications are generally large machines consisting of multiple turbine stages. In such machines, high pressure fluid flowing through the turbine stages must pass through a series of stationary and rotary components. Annular, segmented seals mounted on the stationary components are used to control leakage of fluid along the path between the stationary and rotary components. The efficiency of the turbine is directly dependent on the ability of the segmented seals (also referred to as packing segments) to prevent leakage, e.g., between the rotor and stator. In certain designs, springs maintain the packing segments radially outwardly of the rotor, for example, during start-up and shutdown. After the rotor has been brought up to speed, fluid pressure is supplied between the packing segments and a cavity in the rotor housing behind the segments to displace the segments radially inwardly to obtain smaller clearances with the rotor.
In the exemplary embodiment, the annular seal ring segments, or packing segments, are secured by dovetail type arrangements to stationary nozzle diaphragms located axially between adjacent rows of buckets on wheels that rotate with the turbine rotor. During unit startup and shutdown, one or more compression springs located between the retractable packing segments and the stationary diaphragm produce forces upon the segments that increase the radial clearance between the packing segments and the rotor. When a sufficient pressure drop occurs between startup and shutdown, the pressure-force exceeds the resisting forces of the spring(s), thereby decreasing the radial clearance. This pressure force is made possible by the introduction of steam through steam feed holes in the packing segments. These holes are typically drilled in the packing segments, opening on the high pressure sides of the segments, to allow the steam pressure to build in the cavities behind the segments. Conventionally, these feed holes are drilled axially on the steam flow side, and radially on the back face of each packing segment, meeting internally of the segment, thus creating a 90xc2x0, L-shaped thru hole. This arrangement, however, requires multiple steps in manufacturing, and the sharp turn in the passageway becomes a location for solid particle erosion and/or build up. The latter will hinder turbine performance over time.
This invention relates to a new arrangement for steam feed holes in retractable positive pressure packing segments. In this design, there are one or more holes (as needed) in each packing segment passage, having an angled centerline relative to the packing body. By drilling a single, angled steam feed thru-hole, the L-shaped hole multi step manufacturing process is eliminated, reducing manufacturing time as well as solid particle build up. This new feed hole design also results in a stronger packing segment, compared to conventional steam feed hole designs.
Accordingly, in one aspect, the invention relates to a packing segment for an annular seal ring assembly for use in a hot gas path of a turbomachine, the segment comprising a sealing face mounting a plurality of axially spaced sealing teeth; a center portion radially outward of the sealing face; and a mounting portion radially outward of the center portion, the mounting portion having a radially outermost face; and at least one steam feed hole extending angularly from a first location on the radially outermost face to a second location along a side of the center portion such that, in use, at least a portion of the feed hole is exposed to gas in the gas path for flow through the feed hole to a cavity area behind the segment.
In another aspect, the invention relates to an annular seal ring assembly for a turbine nozzle diaphragm comprising a plurality of part annular packing segments adapted to seat in a dovetail groove in the diaphragm, with a cavity radially between a back face of the segment and the diaphragm, each segment comprising a sealing face mounting a plurality of axially spaced sealing teeth; a center portion radially outward of the sealing face; and a mounting portion radially outward of the center portion, the mounting portion having a radially outermost back face; and at least one steam feed hole extending angularly from a first location on the radially outermost face to a second location along a side of the center portion such that, in use, at least a portion of the feed hole is exposed to gas in a hot gas path for flow through the feed hole to a cavity behind the segment to thereby displace the packing segment in a radially inward direction.